I had similar problems with the chain coupler in my Borg Warner. My problem was that the connecting link in the chain had failed. I did some reading online about how to measure drive chains, measured it, and found the link I needed on Amazon, of all places. Here is a link to the amazon item I bought, though it's currently unavailable. Size on my chain is 40-2.
https://www.amazon.com/dp/B00NP5KG3I...roduct_details
Here is a link to info on measuring drive chains, in case yours is different...
https://www.peerchain.com/how-to-measure-chain-size/